Been trying to figure out whats wrong with the standard radio, i saw that the previous owner had 2 rear speakers and i followed the wires and the leads weren't connected

So im thinking it wasn't working because there was no speakers set up!

But then i looked at the back and it wtf'd me hard

(BELOW: MS41 Radio)

The two white wires are the rear speakers, and (going by the way the pictures facing us) the top left black wire seems to be the antenna, the grey wire with 2 prongs is a function where people in the rear passenger seat can change the volume, and the blue one seems to be the one thats wired up to a knob where it says "Radio" and different dials labeling "DOWN, OFF, ON, UP" that it can be set too

And i figured it out, the two wires were speaker wires that connected too a portable cassette player he had.. and as for the red circle no idea - i'm running another headunit anyway and that radio is still in it's original place so who cares